The present invention relates generally to movement of an aircraft during ground-based operations. More particularly, the invention relates to an electric taxi system (ETS) for moving an aircraft away from a terminal gate.
In traditional commercial aircraft operations, an aircraft may be positioned at a terminal gate for discharging and loading of passengers. After completion of loading, a ground-based tractor or tug may be employed to push the aircraft in a reverse direction away from the gate and to move the aircraft into a position from which the aircraft may begin taxiing under its own power. Use of such tugs contributes to increased operational costs. In some instances a tug and its operator may not be readily available at a desired aircraft-departure time and such unavailability may result in operational delays.
Comprehensive electric taxi systems (ETS) are currently being developed for modern aircraft. Such systems may employ multiple electric motors to drive landing gear wheels during aircraft ground movement and taxiing. An aircraft equipped with such a comprehensive ETS may be able to move away from a gate under its own power without a need for a tractor.
In a typical comprehensive ETS, electrical power for the motors may be supplied from an auxiliary power unit (APU) of the aircraft. Main engines of the aircraft may remain off while the aircraft is propelled on the ground by the electric motors, thus saving the expense of fuel. Substantial weight may be added to an aircraft by installation of a comprehensive ETS. This added weight may result in added in-flight fuel consumption.
Consequently, not every commercial aircraft is a good economic candidate for a comprehensive ETS because of an economic trade-off, between ground-level fuel savings, added in-flight fuel cost and the cost of installing an ETS. An aircraft that makes many short flights in a day may realize overall fuel cost savings because it may spend much of its work day performing ground level movement. The cost of installing an ETS in such an aircraft may be economically justifiable. An aircraft that is employed in long-haul routes may suffer added overall fuel cost by carrying the weight of a compressive ETS over its long routes. Such an aircraft may not be a candidate for a comprehensive ETS.
Thus, even though the development of comprehensive ETS systems may result in some reduction of tug use for some aircraft, there may remain many aircraft for which a comprehensive ETS is not economically justifiable. These aircraft without a comprehensive ETS may still require tug use.
As can be seen, there is a need for system that will allow an aircraft to depart from a gate and move at low speed into a position from which the aircraft may begin taxiing under its own power without use of a tug. More particularly, there is a need for such a system that may be installed on an aircraft at a low enough cost and with a low enough weight so that it may be economically justifiable for a wide range of aircraft, irrespective of utilization patterns of the aircraft.